This invention relates to variable capacity vane compressors, and more particularly to a vane compressor of this kind which is capable of controlling the back pressure acting upon vanes in response to operating conditions of the compressor.
Vane compressors of the type which is capable of varying the capacity thereof and adapted for use in air conditioning systems such as car coolers generally have a plurality of housing cavities defined between the pump housing and the rotor received therein. For reduced capacity operation, at least one of the housing cavities is kept disconnected from the suction chamber to prohibit fluid compression in the at least one housing cavity. Variable capacity vane compressors of this kind have been disclosed e.g. in Japanese Provisional Patent Publications (Kokai) Nos. 56-138489, 57-153982, and 57-102596.
In such vane compressors, vanes are radially slidably fitted in slits formed in the rotor within the pump housing and are pushed radially outward by a centrifugal force produced by the rotation of the rotor and the pressure of compressed fluid introduced as back pressure into back pressure chambers formed in the rotor through gaps between the rotor and the side blocks of the pump housing as well as gaps between the vanes and the slits so as to have their radially outer ends in sliding and urging contact with the camming inner peripheral surface of the pump housing.
However, in such a vane compressor having a plurality of housing cavities, the back pressure chambers communicating with respective vanes in the housing cavities are communicated with each other by means of an annular groove formed in the rotor, as disclosed e.g. in Japanese Provisional Patent Publication No. 57-153982 referred to above. Consequently, even when the fluid compression is prohibited in part of the housing cavities, part of the compressed fluid is introduced into back pressure chambers corresponding to vanes moving in the housing cavity in which the fluid compression is prohibited, so that the vanes moving in the above housing cavity are urged against the camming inner peripheral surface of the pump housing with a large urging pressure. This results in large power loss of the compressor as well as in a great amount of wear of the pump housing and the vanes. No solution to this problem has been provided by any of the aforementioned publications.